4948 -- 시간초과(수정필요)

import sys
sys.stdin = open("input.txt","rt")

while True:
    lists = []

    a = int(input())

    if a == 0:
        break

    for i in range(a+1, 2*a +1):
        cnt = 0


        for k in range(2, int(i**0.5)+1):
            if i%k == 0:
                cnt += 1 # 소수 아님
                break

        if cnt == 0:
            lists.append(i)

    print(len(lists))

    lists.clear()
    
    -------------------
    # 1차 수정
    
import sys
sys.stdin = open("input.txt","rt")

while True:
    lists = []

    a = int(input())

    if a == 0:
        break

    tmp = ""

    for i in range(a+1, 2*a +1):
        cnt = 0


        for k in range(2, int(i**0.5)+1):
            if i%k == 0:
                cnt += 1 # 소수 아님
                break

        if cnt == 0:
            tmp += "*"

    print(len(tmp))
    
    ------------------------
    # 3차 수정
    
    import sys
sys.stdin = open("input.txt","rt")



while True:
    a = int(input())

    if a == 0:
        break


    sosu_cnt = 0

    for i in range(a+1, a*2+1):
        cnt = 0
        for j in range(2, int(i**0.5)+1):
            if i%j == 0:
                cnt += 1
                break

        if cnt == 0:
            sosu_cnt += 1

    print(sosu_cnt)